Protein kinase C (PKC) enzymes are a family of serine and threonine protein kinases involved in apoptosis (14,15), cell proliferation (16-18), secretion (19), and disease states, including ischemic heart disease (4, 20-22) and stroke (23,24). PKC activation involves binding to negatively charged phospholipids and phosphatidylserine. Different PKC isozymes have different sensitivities to other modulators, including Ca2+ and lipid-derived second messengers, such as diacylglycerol (25). Following activation by one or more binding events, PKC isozymes are known to translocate from the soluble cell fraction to the particulate cell fraction (26) containing cell membranes, nuclei, mitochondria, and other components (27,28).
The primary amino acid sequence of PKC can generally be separated into two domains: (i) the N-terminal regulatory domain and (ii) the conserved C-terminal catalytic domain. The regulatory domain includes the C1 and C2 domains, which mediate interactions with second messengers and phospholipids, and generally modulate inter and intramolecular protein-protein interactions. Differences in the primary amino acid sequence, order, and number of copies of signaling domains, contribute to the different activity and/or specificities of different PKC isozymes (25,30). C2 domains in at least one PKC subfamily were called region “V1” until homology to the C2 domains of other family members was recognized (29).
A small region of the C2 domain has been shown to modulate protein-protein interactions (2,5). In particular, several peptides derived from a region of the C2 domain were shown to act as competitive inhibitors of PKC (1). A peptide that interfered with interactions between εPKC and its anchoring protein, εRACK, inhibited εPKC activity (5). A peptide the interfered with auto-inhibitory intramolecular interactions increased PKC activity and reduced ischemic death in an animal model for ischemic heart disease (4,5,7). Related 6-10 amino acid peptides from the same region of C2 were identified (5,22,31-34) and shown to be selective and effective in regulating the biological activities of the corresponding PKC isozymes.
Such studies are limited to a small region of the C2 domain. The need exists to identify other regions of the C2 domain that modulate PKC activity, and to develop selective peptide inhibitors based on such regions. Such peptides are candidates for drug development (6,9,10,12,18,23,28,35-41).